Home » Fish Guides » Why are my Zoanthids not opening? | 9 Reasons To Consider |

Why are my Zoanthids not opening? | 9 Reasons To Consider |

Zoanthids not opening is the main problem faced by many aquarists. However, you can solve this problem easily, and further, you can prevent it even more efficiently. To know each and every reason why about it, keep reading this article. 

Zoanthids not opening

Why Are My Zoanthids Not Opening? 

Zoanthids are commonly found in the deep sea and many other marine environments around the world. Also, they can prepare colonies that have numerous wonderful colors. Thus, zoanthids are a famous organism in saltwater reef tanks. But because of some circumstances, they are closed. Here I mentioned the most common reasons why zoanthids are not opening. You will have a better understanding of it after reading the below paragraphs.  


Firstly, the main reason is the invertebrates in your reef tank. These invertebrates are crawling on the zoanthids. However, zoanthids do not like this practice. Normally, invertebrates like hermit crabs and cleaner shrimp are common members of a reef tank. Also, they are not like to be stable in only one place in the tank. Thus,  they swim around the tank. So, walking or running these invertebrates across a colony of zoanthids is a common thing. This behavior will be a reason to close up the zoanthids corals. Then, zoanthids take some time to open it again. But do not worry. Usually, it does not take much time to open. 

Disturbance Of Fish 

If fish is picking at the zoanthids, it will cause them to close up the zoanthids. Generally, you can see fish in the reef tank. Especially Tang and Clownfish. So, there is a possibility to fish may bother your zoanthids. As a result of this, zoanthids will be unhappy, and it will take time to open. To overcome this, you can move the particular fish into another tank. However, do not worry. because zoanthids closing is not common, but it can happen from time to time. 

Poor Water Parameters

Poor water parameters are another main reason associated with zoanthids opening. Here, the salinity level of the reef tank is a crucial factor. Because, if the salinity level of the tank water fluctuates rapidly, then zoanthids will not open. Moreover, fluctuations of other vital water parameters such as pH and alkalinity can be caused to keep your zoanthids close. So, if you have any issues with the water parameters, you should test and settle them. Then zoanthids will open again nicely. 

Newcomer Or Lack Of Accumulating 

If your zoanthids are new to your reef tank, they will take some period to open. Because they need time to adjust to their new environment. Thus, after purchasing the coral, please do not put them directly in your main reef tank. Because it can be stressful and fatal to your zoanthids. Hence, you should follow the acclimating process before putting them into the main reef tank. 


Due to the actions of pests, zoanthids do not open up. There are common pets that can be found in zoanthid colonies. They are;

  • Sundial snail
  • Asterina Starfish
  • Zoanthid eating nudibranchs
  • Zoa spiders

However, it would be best if you quarantine the newcomers before adding them to the main tank. Further, it is the best preventive method to ensure the specimen free from pests. 


Simply this can be defined as chemical warfare. When you place your zoanthids in your reef tank, you should highly consider their neighbors. Especially, do not place them closely. If not, they tend to emit toxins. Therefore, you should be highly aware of the compatibility of the species. 

Incorrect Flow 

Generally, zoanthids need a medium to high flow rate. Also, high flow helps zoanthids to open. But too many high and low flow rates cause to generate an unhappy zoanthid. 

Incorrect Lighting 

If you place your zoanthids in the tank with high lighting conditions, they will be unwilling to open. Because zoanthids prefer to live in moderate lighting conditions. 


If zoanthids do not like the place where you placed them, they will refrain from opening. So, if there are no above mention issues, you can replace them with their preferable condition. 

Zoanthids not opening

How Do You Get Zoanthids To Open?

Mainly if your zoanthids are happy and healthy, they will tend to open automatically. Further, you can encourage zoanthids to open by following the below methods. The important thing is if you care for them properly, you do not want to pay additional effort for zoanthids. Further, You should feed them nutrients rich feeds to keep healthy zoanthids. Hence, you can provide the below foods to them 

  • Coral reef food, 
  • brine shrimp, plankton, and copepods
  • Rotifer 
  • Lancefish
  • lancefish

Further, you should provide appropriate sunlight to them. Rather than these factors, vitamin and amino acid supplements help to keep them healthy and happy. On the other hand, water conditions also play an important role in generating a healthy zoanthid. Thus, it would help if you eliminated the nitrate, nitrite, ammonia, and phosphate levels in your tank water. Moreover, you should create a peaceful and stress-less environment for your zoanthids. 

How Long For New Zoanthids To Open?

Generally, new zoanthids take 1-2 days to open. This period depends on how fast they adjust to the new environment. But If your new zoanthids do not open up within 1-2 days, there is a reason. At this time, you should consider the tank conditions or parameters. Also, make sure that there is no stressful matter in the tank. However, if there are some issues, you should eliminate them as soon as possible. 

Zoanthids Water Parameters

Normally zoanthids belong to the tough coral category. However, you should maintain water parameters at the optimum range to create a happy and healthy coral. So, you should highly consider the below-listed water parameters in the zoanthid tank. 


The ideal temperature is between 72-78 oF. Also, you should maintain a stable temperature level in your reef tank. However, to accomplish this task, you may need an aquarium heater.  

pH Level

You should maintain the pH level of the reef tank between 8.1 to 8.4. Similarly, it would be best if you kept pH at a constant level. 

Water Salinity Level

 The salinity level of the zoanthid tank should be between 1.023-1.025

Alkalinity Level

In addition to the above water parameters, the alkalinity level that derives the water hardness is should have between dKH 8-12

Calcium Level

you have to meet the ideal calcium level of 350-450 ppm to keep a happy zoanthid. 

Magnesium Level

The ideal magnesium level for zoanthid should be 1250-1350 ppm

Nitrate Level

You should keep the nitrate level below 5 ppm. However, do not let it rise to this level. 

Phosphate Level

It is best to keep the phosphate level of water below 0.03 ppm in your reef tank. Overfeeding is the major reason that increases phosphate levels in tank water.

Ammonia Level

You have to eliminate the ammonia level of your tank. Because it can harm your zoanthids. So, always try to maintain ammonia levels below 5 ppm.

coral problem

How To Know If Zoanthids Are Dying

If your zoanthids do not tend to open for an extended period, you will check them carefully because they may be dead. Further, if you notice that they are losing their colors and melting away, these are the signs that appear when they die. However, zoanthids are pretty rough. But do not give up on them. Because they may die because of your bad maintenance. In addition to that, when they tend to die, you can appear these signs too. 

  • You can see collapsed and wilting over zoanthid polyp
  • Disintegrating polyp of zoanthids that can shred apart 
  • You can feel a foul odor
  • Zoanthids will appear with dark pigmentation and coloration

Why Zoanthids Are Dying?

There are several reasons to die your zoanthids. Here I mentioned the main and most common causes. 

Poor water condition

Poor water parameters tend to generate an unhappy zoanthid. So, you should maintain the optimum water parameters in your tank. If not, it will be fatal to your zoanthids. The main reason for poor water condition is bioload. As a result of high bio load, byproducts such as nitrate, nitrite, and ammonia will generate. So, you should avoid overfeeding. Also, you have to perform water changes regularly. 

Improper placement 

If you place your zoanthids without enough space, it will cause chemical warfare. It means that there can create chemical warfare among corals due to territorial issues. 

As a result of this, zoanthids tend to strike foods. However, eventually, it can be fatal. 

Lack of nutrients 

Further, if you do not provide enough nutrients to them, they will be weak. Because of that, you should feed them enough quality food. 


When they get diseases, and if you do not treat them properly, they will die. 

Too much high or low flow rate

Zoanthids like to live with a moderate to high flow rate. So, if you do not provide this range, they will be unhappy. Further, if you do not offer a preferable flow, it can be a reason for the death of zoanthids. 

Too much high lighting conditions

Generally, the ideal lighting condition for zoanthids is moderate. However, if zoanthids live in high lighting conditions, they will tend to stress and die.

Zoanthids Health Tips

If you like to keep your zoanthids happy and healthy, you can go through the following tips. 

Feeding Tips 

If you feed them well, you can improve their color, growth rate, and overall health. Also, periodic feedings are beneficial for zoanthids. So, you can go with the target feeding. Moreover, it is better to feed them a few times per week. Further, quality foods are also an added advantage for your zoanthids.

So, you can feed them by using plankton, copepods, krill, and brine shrimp. On the other hand, zoanthids have the ability to grab nutrients from the water column. Hence, if you like to go without the target feed, you can provide coral foods like reef roids. Similarly, you can add them into the high flow area in your reef tank. 


Generally, zoanthids can tolerate a variety of lighting conditions. But they like to live in a place that has medium to high lighting conditions. This ideal condition helps to enhance their colors. Further, it encourages growing their polyps. But be aware that the aquarium light is not too intense. Then it can cause a loss of the colors of your zoanthids. Further, you can meet the ideal range by using quality reef LED light, metal halides, or T5. Additionally, blue actinic LEDs or bulbs can be used to get some of the best colorations. 

Water Flow 

Zoanthids live happily in low to moderate flow with varied patterns. The beat water movement helps to open their polyps and show their actual colors. 

coral problems

Zoanthids Not Opening All The Way

If your zoanthids do not open all the way for a long time, you have to lose your hopes. Because your zoanthid is already dead. However, you can ensure this by observing them clearly. Because when zoanthids are dying, they lose colors and melt away. 

Why do New Zoanthids Not Opening

Typically zoanthids take a few times to adjust to the new environment. But after adjusting, they tend to open up. However, if they are not open, there are some issues with your water condition, flow, lighting, placement, pests, invertebrates, or others. So, you should seek and find the particular issue. Then you can overcome it immediately to survive your zoanthids. 

How Long Does It Take For zoanthids To Open Up After Adding To A New Tank?

Generally, your new zoanthids should open within 1-2 days. But if not, there can be an issue with your setting. 

Why Are Utter Chaos zoanthids Not Opening?

If you search clearly, you can find a reason that includes in the below list. 

  • Issues with your water chemistry 
  • Disturbance of fish and invertebrate 
  • Pests 
  • Poor lighting condition 
  • Improper water movement 
  • Unhappy placement  
  • Allelopathy 
  • Issues with placement 

Why Are Palythoa Grandi’s zoanthids Not Opening?

Similarly, the palythoa grandis does not like too high-water flow. So, if you place them under a high flow, they avoid opening up. Further, when you move your palythoa grandis around, they take time to adjust and open. Also, you should check them and verify whether the algae grow on them or not. Because algae also lead them to stay close. 

Moreover, you should make sure your palythoa grandis live in moderate to high lighting conditions. Because they do not open up due to low or too much lighting conditions. Also, pests such as Sundial snails, Asterina Starfish, Zoanthid eating nudibranchs, and Zoa spiders affect palythoa grandis badly. In addition to these issues, this can happen due to poor water chemistry and allelopathy.


There are many reasons for the question “why your zoanthids are not opening?”. The main causes are poor water conditions, pests, invertebrates, poor lighting, and flow, etc. However, I hope now you have better knowledge to overcome this issue. So, This is the best time to decorate your aquarium with wonderful zoanthids. They will add an excellent look to your aquarium. 

Read Next: Can Mandarin Goby and Clownfish Live In The Same Tank? | 8 Fun Facts |

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About Dr.Chamika

Hello, I'm Dr. Chamika. I am a Researcher in Water quality, Aquatic organisms, and Environmental chemistry. I am a passionate fish keeper, with10 years of experience. My mission is to help other aquarists experience the joy of fish keeping.